A number of previously known infiltration methods have been used to produce multicomponent ceramics or ceramic composites. These methods include: (1) metal-matrix infiltration, (2) melt processing, (3) chemical vapor infiltration (CVI), (4) nitridation, (5) chemically bonded ceramic processing, and (6) ceramic hardening infiltration.
All six methods may be used to infiltrate a previously shaped ceramic particulate porous matrix or preform (commonly referred to as green body). However, the porosity of the initial fiber or preform in these methods often needs to be minimized at the beginning of each process so that the shape of the sintered product does not differ substantially from that of the initial preform.
The importance of an infiltration medium for creating a bonded monolithic structure as well as increasing or lowering the density of a monolithic body has been described in U.S. Pat. No. 8,114,367 and U.S. patent application Ser. No. 12/71,513 via a method described collectively as hydrothermal liquid phase sintering (HLPS) that can be performed at relatively low temperatures and low pressures.
In many cases, it is desirable for the ceramic or ceramic composite product to have a uniform microstructure with respect to phase and composition. It is also desirable to conduct HLPS reactions in a relatively short time frame instead of a long time frame, such as in the case where large thick monolithic bodies are required for various applications, such as for roads or bridges. For this reason, it is desirable to balance the rate of reaction and mass transport for the HLPS method.
For example, low temperature solidification carbonation technology is a promising replacement for Portland cement technology because it produces hydrate-free cement (HFC). Unfortunately, the solidification process requires the delivery of liquid water and gaseous CO2 in every region of the microstructure. This can be troublesome for several reasons. First, thick microstructures can limit the transport of either of these components. Second, there are remote regions where supply of CO2 or water could be scarce or costly. Third, the amount of CO2 required in systems where a high degree of carbonation is required is extensive. For example, an 11-inch thick 30-ft wide roadbed that has 10 wt % HFC carbonated at about 50% requires 282 tons of CO2 per mile. This amounts to about 7-14 truckloads of liquid CO2. Thus, shipping this much CO2 implies that there could be logistics problems associated with its delivery. Looking at water, the main problem with this component is being sure that the liquid is uniformly distributed and partially fills the pore volume so that gas diffusion can occur simultaneously. For thick beds of road, both liquid and gas transport must be accommodated simultaneously. Given the pore size of packed particle beds and the substantially larger viscosity and density of fluids compared to gases, there is a problem that a percolation network of filled pores can create a barrier to CO2 transport, thus inhibiting the carbonation process.
Thus, the strategy for the precursor choice (i.e. solvent and reactive species) and method of introducing the precursors comprising the infiltration medium is critical.